This invention relates to a vehicle suspension system and more particularly to a damping system for controlling the motion of a pair of independently suspended vehicle wheels so as to provide interrelationship between their action for controlling vehicle movement.
Vehicle suspension systems have been proposed that embody individual hydraulic dampers associated with each of the wheels for damping their respective motion. As a further improvement upon this arrangement, systems have been proposed wherein pairs or more of wheels may be interrelated so as to control roll and/or pitch of the vehicle in addition to the individual wheel damping when encountering road objects. Various systems have been purposed for accomplishing this effect, many of which become quite complicated in nature and in construction.
There has been proposed, however, an interrelating system between pairs of wheels suspensions wherein the interrelationship is accomplished in a simplified manner and yet which provide good control not only of the individual wheel movements when encountering individual obstacles but also for controlling vehicle movement during such things as cornering, breaking or acceleration wherein pitching may occur.
One particularly advantageous type of system and numerous embodiments of it is disclosed in U.S. Pat. No. 5,486,018 issued Jan. 23, 1996. In the systems shown in this patent, each wheel is associated with a hydraulic damper that is comprised of a cylinder in which a piston reciprocates. The cylinder is connected to either the wheel or vehicle body and the piston is connected by a piston rod to the remaining vehicle component. The piston divides the cylinder into a pair of fluid chambers one of which may be considered to be a working chamber and the other of which may be considered to be a reservoir chamber. A damping valving arrangement is provided for controlling the flow between the working cylinder portion and the reservoir chamber. Thus, the individual units act like conventional shock absorbers.
However, the piston rod displaces a volume in one of the chambers and thus, it is necessary to provide a reservoir where makeup fluid may be added and subtracted to compensate for this piston rod displacement. In accordance with the embodiments disclosed in that patent, pairs of wheels have a common reservoir arrangement which acts as a pressure control system. The makeup fluid from each unit is transmitted to a respective variable volume chamber and the moveable elements of those two chambers are interlinked to each other so as to provide additional suspension control between the two associated wheels for controlling vehicle body movement. This can be utilized to reduce roll and/or pitching.
For example, if the associated or interconnected wheels are at opposite sides of the vehicle, when both wheels strike an obstacle, each piston and cylinder of the shock absorbing unit will undergo the same movement in the same direction. The differential fluids are transferred between the pressure control device and will cause equal displacements of the moveable members that are interlinked and the system operates as a conventional suspension system.
If, however, the vehicle rounds a curve, one suspension unit, on the outside, will tend to be compressed while that on the inside will tend to expand. Thus, there is a differential flow of fluid between the units and the interconnection provides further damping control resisting such body motion.
The difficulty with this type of system is that the requirements in terms of size and capacity of the individual shock absorbers is a different value for optimum damping when equal displacements take place during normal straight ahead movement than when rounding a curve. Similar situations are true with respect to front and rear interconnected suspensions for damping pitching movements during acceleration or braking.
That is, when the pressure control device is acting to dampen body movements between the two wheels, the pressure control device works in combination with the respective shock absorbers. Because of this, the individual wheel shock absorbers should be made somewhat smaller to reduce their effect on the overall body control. Thus, the individual shock absorber design tends to be a compromise between the optimum for these two different damping conditions.
It is, therefore, a principal object of this invention to provide an improved suspension system for interrelated wheels of a vehicle that provides optimum damping under all types of conditions.
It is a further object of this invention to provide an improved vehicle suspension system for a vehicle wherein the damping arrangement is optimized for each type of condition utilized in a simple but effective manner.